A "hot tap" in the fluid handling industry is a procedure for establishing an opening in a pipeline while the pipeline is under pressure and in service and which permits such activities as branch line connection, repair bypass connections, etc. Hot tap connections are performed to permit uninterrupted service of the primary flowline during the line tapping procedure. Hot tap connection procedures eliminate the necessity of shutting down the main flowline, thereby eliminating loss of flowline production.
A hot tap connection procedure is conducted by first welding or otherwise attaching a pipe connection saddle to the flowline which incorporates a flange for bolted connection of a hot tap valve thereto. Aa pressure-containing dome with an internal cutter is then secured to the hot tap valve to thus provide a sealed enclosure including the valve chamber of the hot tap valve. Thereafter, pressure in the dome is balanced with line pressure and the valve is opened thus permitting the cutter to be extended through the valve and rotated against the flowline, thereby cutting an aperture in the flowline. In some cases pressure balancing occurs during the line cutting operation. In this case, as soon as the flowline is cut through, pressure from the flowline enters the hot tap valve and a dome and becomes equalized with respect to the flowline. After the hole cutting operation has been completed, the cutter is retracted from the valve and the valve is closed to thus isolate the pressure-containing dome from line pressure. Thereafter, pressure is bled from the dome to equalize the dome with atmospheric pressure. The dome and cutter mechanism then may be removed from the valve to thus permit connection of a branch line conduit, bypass conduit, etc., to the valve.
Especially in the case of hot tap type bypass repair operations, it is typical to remove the hot tap valve after the repaired line has been placed back in service. As is the case with most hot tap valves, the resilient elastomeric face sealing member incorporated within each of the valve seats becomes highly worn or deteriorated due to the pressure of metal cuttings resulting from the hole cutting procedure. In many if not most cases hot tap valves may be utilized only once before they must be disassembled in order to replace the sealing elements of the seat members or to replace the seat members themselves. Because of the large numbers of bolts that typically are utilized to secure a sandwich type hot tap valve in assembly, disassembly, repair and reassembly of hot tap valves is an extremely time consuming and expensive procedure. It is desirable therefore to provide a hot tap valve mechanism which is designed to provide service personnel with the capability of replacing the elastomeric resilient sealing members of the valve seats thereof without necessitating disassembly and reassembly of the valve mechanism.